The present invention relates to an image capturing method and apparatus for capturing the shape of a target object as image data, and a fingerprint collation method and apparatus which detect a fingerprint ridge/valley pattern as image data by using the image capturing method and apparatus and perform collation.
In performing fingerprint collation, to improve collation precision, a fingerprint image must be captured to obtain a clear image of a fingerprint ridge/valley pattern. Fingerprint sensors used to capture fingerprint images in a fingerprint collation apparatus of this type include an optical fingerprint sensor, capacitive fingerprint sensor, and the like. A fingerprint sensor is designed to detect a fingerprint ridge/valley pattern as optical refractive index differences or capacitive value differences and generate the pattern as a halftone image.
According to the above fingerprint collation apparatus, when a user is to be authenticated by using a fingerprint, the fingerprint data of the user is registered in advance. In this state, a fingerprint image of the user is acquired by the fingerprint sensor, and fingerprint data is generated. The generated fingerprint data is then compared with the registered fingerprint data. If they coincide with each other, the user is authenticated.
The skins of human fingertips vary in state among individuals. For example, some persons have dry fingers, and others have fatty fingers. In addition, the state of the skin of a fingertip of a given person changes depending on seasons and physical conditions. In a conventional fingerprint collation apparatus, fingerprint images which change for the above reasons are detected under the same condition, and hence accurate fingerprint images required for collation cannot be obtained. If an image in a desired state cannot be obtained, accurate fingerprint collation cannot be properly performed.